1. Field of Invention
The present invention relates in general to electric motors, and more particularly to electric motors of a two rotor single stator type which comprises outer and inner rotors which rotate around and within a common stator. More specifically, the present invention is concerned with a stator for the two rotor single stator type electric motor.
2. Description of Related Art
One electric motor of the above-mentioned type is shown in Japanese Laid-open Patent Application (Tokkai) 2000-14086. In the electric motor of this published application, upon feeding a compound electric current to a common stator, two rotors, that is, inner and outer rotors are rotated relatively around and within the common stator. By controlling the compound electric current fed to the stator, rotation of the inner rotor and that of the outer rotor are individually controlled.
Usually, the stator used for such two rotor type motor is of a cantilever type wherein a torque produced by each rotor is received by only one axial end of the stator that is secured to a case that constitutes a structural base. Thus, under operation of the motor, the torque produced by each rotor causes generation of a certain torsional stress applied to the stator in a direction to induce a deformation of the same. Thus, if the stress is great, the stator is subjected to a deformation.
FIGS. 11A and 11B of the accompanying drawings schematically show the stator 301 that is disclosed by the published application. That is, as is seen from FIG. 11A, the stator 301 comprises a stator core that includes a plurality of stator teeth SP that are circumferentially arranged around a common axis of the motor at evenly spaced intervals. Each stator tooth SP has a rectangular parallelepiped shape and includes a plurality of pressed flat magnetic steel plates that are closely aligned along the common axis intimately and closely contacting to one another. Thus, upon assembly, the stator core has a waterwheel shape that has a plurality of stator teeth SP circumferentially arranged about the common axis. Each stator tooth SP has a coil that is put therearound making round-trips in a direction parallel with the common axis. The stator core thus assembled is sandwiched between two axially spaced supporting brackets 303A and 303B and tightened by a plurality of bolts 304 and nuts 305. Although not well shown in the drawings, finally, two supporting brackets 303A and 303B, bolts 304 and nuts 305 are all embedded in a molded plastic to constitute the cylindrical stator 301.
As is seen from FIG. 11B, under rotation of the outer and inner rotors, a certain torque is inevitably applied to the stator 301 in a direction to induce a deformation or inclination of the stator teeth SP for the reason as is mentioned hereinabove.